This invention relates to a sheet processing apparatus which receives sheets whereon an image is formed by an image forming apparatus such as an electrophotographic copying machine, a printer, or a printing machine and discharges them onto a receiving tray by a discharging means after finishing processes such as inverting upside down, stacking, and binding together.
For an apparatus which collates a plurality of sheets with an image formed by an image forming apparatus ejected from the apparatus for each set of copies and binds them with a stapler, a sheet processing apparatus, called as a finisher, is used.
This finisher is functionally connected to an image forming apparatus such as a copying machine, or a printer, and is designed to be driven corresponding to the sequential operation of the copying or printing process.
Accordingly, for an image forming apparatus capable of forming images at a high speed and for a high volume, it is required that the finisher be capable of high-speed and high-volume processing which can fulfill the function in accordance with the processing speed.
Concerning such kind of a finisher capable of high-speed processing, several proposals have already been disclosed in the Japanese laid open patents S60-142359, S60-158463, S62-239169, S62-288002, S63-267667, and H2-276691, and Japanese publicized patent H5-41991.
The sheets with an image formed on them, conveyed out of the image forming apparatus mainframe, are successively stacked in an intermediate stacking plate in the collated order, and are subjected to sheet processings such as stapling, etc., after a set of copy sheets are stacked. The bound set of copy sheets are carried on the discharging belt provided at the bottom of said intermediate stacking plate, transported, held between a pair of upper-and-lower ejecting rollers, and are discharged onto the receiving tray.
The sheet processing apparatus described in the Japanese laid open patent H8-42728 is provided with a stapler and a receiving tray corresponding to it. Further, the sheet processing apparatus described in the Japanese laid open patent H7-76190 is provided with two staplers and two receiving trays corresponding to them.
The sheet inverting system described in the Japanese laid open patent H8-85663 has two different positions for positioning the leading edge of sheets, a first one at which stapling is carried out, and at a second one at which stapling is not carried out; these two different positions are determined by a movable finger for position adjusting.
The tray apparatus described in the Japanese laid open patent H1-181672 is provided with a stopping portion made up of a soft member for stopping the trailing edge of the paper sheets stacked on the receiving tray and an urging member for urging one end portion of said soft member upward.
In the conventional sheet processing apparatus, the sheets with an image formed on them, conveyed out of the image forming apparatus, are subjected or not subjected to the processings by the sheet processing means (including stapler, shifting means, bookbinding means, punching means, etc.), transported, and ejected onto the receiving tray by the discharging means, where they are sliding down along the tilted surface of the tray until their trailing edges collide with the stopper to be stopped there. On the other hand, the sheets which are not to be subjected such processings are directly ejected onto the fixedly attached tray where they are sliding down the tilted surface of the tray until their trailing edges collide with the stopper to be stopped there.
In regard to the conventional sheet processing apparatus and the conventional sheet discharging apparatus, the problems to be solved will be described in the following.
(1) The sheets with an image formed on them are transported by the sheet processing apparatus; however, the sheet transport path in the stapling process mode having the intermediate stacking plate is different from the sheet transport path in the non-stapling process mode; hence, the sheet transport path is long and large and has a complex structure, which results in poor sheet transport. Further, because a bifurcating means for switching the path, a number of transport rollers, driving means for these, control means, and so forth are required, there are problems in that the apparatus is made complex and large-sized, and that the manufacturing cost is increased.
(2) In the sheet inverting system described in the Japanese laid open patent H8-85663, there are provided two different positions for positioning the leading edge of sheets, a first one at which stapling process is carried out, and a second one at which stapling process is not carried out; these two different positions are determined by a movable finger for position adjusting. Because this sheet inverting system uses the movable finger for positioning oscillation, there is a problem that it requires a driving source and a driving means, which makes its structure complex and increases the risk of malfunction. Further, because the movable finger oscillates at a fixed position, it is difficult to carry out the positioning of the leading edge of the sheet precisely for all sizes of the sheets from the minimum size (A6R size for example) to the maximum size (A3 size for example).